Automatic industrial means of monitoring tyres developed by manufacturers and intended especially to assist operators responsible for visual monitoring, call widely upon image processing techniques.
The methods employed to perform these processings consist, as a general rule, in comparing a two-dimensional or preferably three-dimensional image of the surface of the tyre to be inspected, with a two-dimensional and preferably three-dimensional reference image of the surface of the said tyre.
One of the steps of this process consists, in a known manner, in acquiring the three-dimensional image of the surface of the tyre, with the aid for example, of means based on the principle of optical triangulation, implementing for example a 2D sensor coupled to a lighting source of laser type.
The topographic image of the surface of the tyre is as a general rule a two-dimensional image, termed a grey level image, in which, with any point, i.e. with any pixel (x, y) of the image, is associated a value f(x, y), called the grey level, which represents the altitude of this point with respect to the surface. This grey level value can usefully be coded on 8, or 16 bits or indeed 32 bits for better dynamic range. For coding on 8 bits, the value 255 (white) corresponds to the highest altitude, and the value 0 (black), corresponds to the lowest altitude.
The continuation of the process for analyzing the image obtained then consists, inter alia, in determining the relief elements of the surface to be inspected. This step is particularly significant within the framework of the analysis of the internal part of the tyre in that, the striations or the relief patterns intended to ensure the venting of the air during the cooking of the tyre must be precisely located and identified, so as not to be considered to be anomalies of the said surface.
These striations or these relief patterns stand proud by a few tenths of a millimeter from the mean surface of the internal part of the tyre.